A. Summary of the Invention
The present invention relates generally to valves and valve actuators, and more particularly to a valve and actuator that is adapted for automatic shut in during wireline operations.
B. Description of the Prior Art
Valve and actuator combinations are used extensively in various fluid handling systems. For example, valve and actuator combinations are a primary component of surface safety systems used in the control of oil or gas production. Such valve and actuator combinations typically include a gate type valve, which includes a gate having a port and an imperforate portion, which is movable within a valve body between an open position wherein the port is aligned with the valve inlet and outlet, and a closed position wherein the imperforate portion is sealingly interposed between the inlet and the outlet. The actuator in such systems typically includes an actuator stem, which is connected to for reciprocation with the valve gate, and a piston or the like, which is connected to the stem and which is reciprocatingly mounted in a cylinder. Normally, the piston is actuated in one direction by pneumatic or hydraulic pressure to hold the valve in either the open or the closed position, and by spring or internal valve body pressure to the other of the open or closed positions.
Surface safety systems, which include valve and actuator combinations, are commonly used in well heads or christmas trees through which wireline operations are conducted. In wireline operations, various tools are run from the surface into and out of the well by means of a wire. The type of wire used is dependent upon the type of tool that is being used; however, all of the various types and sizes of wire are strong and very durable.
During wireline operations, it is necessary that the safety system that controls the well not be disabled or otherwise rendered inoperative. In other words, it is necessary that the safety valve be able to close to shut in the well when wireline operations are being conducted.
There have been developed a number of wireline cutting actuators for use in combination with surface safety valves. The wireline cutting actuators are designed to provide sufficient closing force, even in the absence of valve body pressure, to shear the wireline and allow the valve to move to the fully closed position. Since the wires used in wireline operations are so durable, very high forces are needed in order to shear the wire. Accordingly, wireline cutting actuators typically are large massive unitary structures that include tremendously strong springs. Such actuators are bulky and hard for workmen to service. More specifically, presently existing actuator designs require normally the length of the actuator for clearance from 30 inches to 50 inches and/or that special tools and special handling equipment be required to move the entire actuator and spring assembly as one massive unit. Usually, two or more persons are required to remove such actuators. The total time required to remove, service, and reinstall such actuator equipment can amount to several hours and require substantial working space and equipment clearance. An example of a presently existing wireline cutting actuator is the Baker CAC Model WC wire cutting hydraulic actuator, which is illustrated at page 572 of the 1982-83 Composite Catalog.
It is an object of the present invention to provide a wireline cutting actuator and actuator valve combination that overcome the shortcomings of the prior art. More specifically, it is an object of the present invention to provide a wireline cutting actuator that may be assembled and disassembled easily and quickly by one person using standard, readily available tools.
It is a further object of the present invention to provide an actuator that may be disassembled with a minimum of clearance.
It is a further object of the present invention to provide an actuator with a light weight easily removable piston housing assembly that permits simple replacement of the seal components during servicing.
It is a further object of the present invention to provide a wireline cutting actuator that has a separate spring assembly which is not affected by the assembly or disassembly of the piston housing assembly.
It is a further object of the present invention to provide a valve that reduces the force necessary to cut a wireline and which prevents the formation of wire fragments within the valve body.